FIG. 1 discloses a typical flow sheet for a two-stage refining process for the manufacture of mechanical pulp. Chips 10 are introduced into a primary refiner 12. In refiner mechanical pulp the chips will be cold when fed to the refiner 12. In thermomechanical pulp the chips will have been presteamed under pressure. The TMP Survey, Pulp & Paper, July 1978, pp. 99-110 states that the presteaming may be from 1-8 minutes, the usual being from 2-4 minutes and the pressure may be from 7 to 45 psi, the usual pressure being from 15 to 25 psi. Chemicals may also be added to the chips. The usual chemicals are hydrogen peroxide, sodium bisulfite, sodium sulfite, alum or sodium hydroxide.
The first stage refiner 12 is a pressure refiner. The TMP Survey states that the pressure in the refiner is from 11 to 40 psi. The consistency of the pulp in the first stage is from 23 to 45% and from 41 to 102 horsepower per daily oven dry ton is supplied to the refiner.
The fibers 14 from the first stage refiner 12 pass to a cyclone 18 in which the steam 20 is separated from the fibers. The cyclone 18 may be atmospheric or pressurized. Pressure cyclones allow steam 20 to be collected in an appropriate heat recovery system. The fibers 26 then pass to the second stage refiner 42 in which the fiber bundles are further defibered. The second stage refiner operates at atmospheric pressure. The TMP Survey states that the consistency in a secondary refiner is from 13 to 40% and from 27 to 68 horsepower per daily oven dry ton is supplied to the refiner.
The fibers 44 then pass to a latency tank 46 in which the fibers are soaked in hot water to remove the latency from the fibers. The TMP Survey shows the pulp consistency in the latency tank to be from 1 to 4.5%, the usual consistency being 2-3%. The time in the tank is from 1 to 120 min., the normal being from 20 to 30 min., and the temperature in the tank is from 57.degree. to 96.degree. C., the normal temperature being about 70.degree. C.
The fibers 48 from the latency tank 46 then pass to a screen 52 in which the rejects, the fiber bundles and other reject materials, are separated from the individual fibers. The rejects are processed in a reject refiner system 54. The rejects from the screens 52 are carried to a reject tank 58. The material 60 from the reject tank 58 is carried to a press 62 which raises the consistency of the fiber mass. The pressate 64 is collected in a filtrate chest for reuse. The higher consistency reject material 66 then passes to a reject refiner 68. The TMP article indicates that the consistency of the material in the reject refiner 68 may be anywhere from 3 to 35%. The fibers 70 from the reject refiner 68 pass to a storage tank 72 and the material 74 from the storage tank is returned to the screen 52. A pump 76 aids in the transfer of the material 74 to the screen 52.
The accepted material fibers 78, from the screen 52 pass to further fiber processing 84 in the mill. This can include bleaching and paper or pulp formation. The material may be used for tissue, board, newsprint, magazine, rotogravure and offset grades of paper, cartonboard and speciality papers. The material 86 is transported from the mill.
FIG. 2 discloses a special refining process for refining 100% aspen chips to a powder like material which is used as a filler in paper. The chips 110 enter a first stage refiner 112 in which they are ground into fibers and fiber bundles. The material 114 from the first stage refiner 112 passes to a latency tank 124 in which the fibers and fiber bundles are treated at a consistency of 4% in hot water. The treated material 126, still at 4% consistency, is transported by a pump 128 to the second stage refiner 142 in which the fibers and fiber bundles are further refined at the 4% consistency. The material 144 from the second stage refiner 142 passes to a second latency tank 146 having conditions which are the same as those in the latency tank 46 of FIG. 1. The material 148 from the tank 146 is moved by a pump 150 to the screen 152. The rejects from screen 152 are treated in the reject refining system 54 which is identical to reject refining system 54. Similar reference numerals are used to denote the same equipment and flows. The accepted material 178 from the screen 152 passes to an additional refiner 180 where it is ground to a flour like material. This material 182 is then used as a filler for paper.
FIG. 3 is a diagram of the Sunds "Compacter" process. The chips 210 pass through the primary refiner 212 and the material 214, fibers and fiber bundles, from the refiner 212 passes to a cyclone 218 in which the steam 220 is removed from the material. The material 226 then moves to a press 230. The pressate 232 is sent to a sewer. The higher consistency material 240 from the press 230 then passes through the second stage refiner 242. The material 244 from the refiner passes to a latency tank 246 where it is soaked and the latency removed. The material 248 from the tank 246 is moved by pump 250 to the screen 252. The rejects from the screen 252 are treated in the reject refining system 254 which is identical to reject refining systems 54 and 154. Similar reference numerals are used. The accepted material 278 from the screen 252 passes through additional processes 284 within the plant and the finished material 286 is transported from the plant.
FIG. 4 discloses a one-stage refining process. In this the chips 310 pass through the refiner 312 and the material from the refiner 312 passes through the cyclone 318 in which the steam 320 is removed. The material 322 from the cyclone 318 then passes to the latency tank 346. The material 348 from the latency tank 346 is moved by pump 350 to the screen 352. The reject refining system 354 and the additional processing 384 are the same as those shown and described in FIGS. 1 and 3 and similar reference numerals are used.
The Opco process is described in "The Opco Process: The Most Flexible Ultra High Yield Pulping Method" by J. E. McDonald; "The Opco Process," Mr. R. A. Leask, Tech '82 Mechanical Pulping Course; and "Ultra High Yield Pulping of Eastern Black Spruce, Part 3, Interstage Sulfanation," by C. Heitner, et al. International Mechanical Pulping Conference 1981.
Canadian Pat. No. 1,145,107 describes a treatment of mechanical pulp.